Organic electronic devices, such as organic light emitting diodes (OLEDs), organic thin-film transistors (OTFTs), solar cells, and other organic material-containing devices, have been attracting a great deal of interest as the devices of the next generation. For such organic electronic devices to be commercialized, high quality passivation layers need to be developed in order to ensure the reliability of the device. The reliability of a device is directly related to the lifetime of the device. Most organic electronic devices that use organic materials are problematic in that they degrade easily by moisture, oxygen, and light existing in the atmosphere and they show very low durability against heat, where their lifetime decreases with a rise in temperature. Accordingly, various methods for blocking the degradation and deterioration of organic materials by moisture and oxygen are being developed.
Among those methods, research on passivation layers for OLEDs has been actively underway. Korean Patent Publication No. 2002-22250 discloses a method of protecting a device by covering its surface with a metal cap or a glass cap in a structure, as illustrated in FIG. 1. In particular, FIG. 1 shows a structure of a prior art organic electroluminescence device, including an anode glass substrate 1, a hole injection layer 2, a hole transfer layer 3, a light emitting layer 4, an electron transfer layer 5, an electron injection layer 6 and a cathode electrode 7, whose surface is covered with a steel use stainless can or a glass lid 9 containing a humectant 8 and sealed with a sealing agent, such as photocurable epoxy. However, since the method is incapable of completely blocking moisture and oxygen transmission after the fabrication of an organic device, there is an urgent need to establish complementary measures. Further, in case of a large area device (30 inches or more), limitations exist with respect to consistent processing schemes and application of the device.
Korean Patent Publication No. 1999-49287 discloses a method of applying ceramic materials, such as Al2O3, MgO, BeO, SiC, TiO2, Si3N4, SiO2 and the like, to a passivation layer. However, the method has several disadvantages in that a high temperature is required for carrying out the process and it is difficult to expect properties that are better than the physical properties of the ceramic materials themselves. Korean Patent No. 540179 discloses a method of fabricating an organic electroluminescence device having an inorganic composite thin layer 11 containing a mixture of SiO2 and MgO at a constant ratio as a passivation layer, where the inorganic composite thin layer is deposited on the surface of the device. FIG. 2 illustrates such an inorganic composite thin layer 11 deposited on the device of FIG. 1, as an alternative to the can or lid 9 of FIG. 1. While such a method is capable of lowering the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) by applying a single inorganic thin film passivation layer to a conventional organic electronic device, the method is problematic in that it is difficult to form a uniform layer and that there is a risk of lower uniformity against moisture and oxygen resistance due to the weak interfacial adhesion strength, which also results in surface light scattering and the deterioration in light transmission.
Meanwhile, plastic substrates require characteristics, such as low profile/small form factor, impact resistance, low thermal expansion rate, and high gas barrier property. The primary issue with applying plastic substrates to display and organic electronic devices is developing a technique for improving the gas barrier property so as to block the transmission of atmospheric gas, such as moisture and oxygen. Plastic substrates made of polymer resin have the advantage of being flexible, but they are problematic in that it is easy for gases, such as moisture and oxygen, to penetrate thereinto because of their inherent properties different from a glass substrate, and they show very weak chemical resistance to a variety of chemical products including various solvents. In order to fabricate a highly functional plastic substrate, the substrate surface must be protected with a substance which exhibits very low moisture and oxygen transmission rates and a high resistance to various chemicals. Further, in order for the plastic substrate to block moisture and oxygen transmission, the thermal stress between the plastic substrate and the ceramic passivation layer must be reduced, and microparticles have to adhere and accumulate on the substrate surface while reducing the surface roughness of the substrate. In order to achieve the above objective, there is a need to develop a passivation multilayer technique of repeatedly laminating an organic material capable of being planarized and a ceramic inorganic material having strong protective properties.
The present inventors have thus endeavored to overcome the problems in the prior art and develop an organic/inorganic hybrid thin film passivation layer. The hybrid thin film passivation layer includes an organic polymer passivation layer made of a photocurable polymer according to a UV/ozone (O3) curing process which is capable of improving surface energy and forming a more delicate surface structure compared to that made by a conventional UV curing process, and an inorganic thin film passivation layer prepared by using a nanocomposite material mixed with two or more inorganic materials in an up-and-down laminated structure. The organic/inorganic hybrid thin film passivation layer of the present invention can effectively block oxygen and moisture transmission, ensuring the stability and reliability of a device and improve the gas barrier property of a plastic substrate.